Barrier coatings

ABSTRACT

THIS INVENTION RELATES TO FIBROUS SUBSTRATES COATED WITH A MIXED LATEX OF POLYVINYLIDENE CHLORIDE POLYMER AND AN ETHYLENE, VINYL CHLORIDE AND ACRYLAMIDE INTERPOLYMER.

United States Patent 3,567,502 BARRIER COATINGS Paul R. Graham, Ballwin, and August F. Ottinger, St. Louis, Mo., assignors to Monsanto Company, St. Louis,

0. No Drawing. Filed Apr. 3, 1968, Ser. No. 718,367 Int. Cl. D21h 1/40 U.S. Cl. 117-155 11 Claims ABSTRACT OF THE DISCLOSURE This invention relates to fibrous substrates coated with a mixed latex of polyvinylidene chloride polymer and an ethylene, vinyl chloride and acrylamide interpolymer.

This invention relates to coated fibrous substrates and to methods of making the same. More particularly, this invention is concerned with novel coated fibrous substrates in sheet and roll form in which the substrate may be paper, paperboard, preformed paper containers, fabric or other fibrous-like bases wherein the coating is laid down from a mixed emulsion of a polyvinylidene chloride polymer latex and an interpolymer latex of ethylene, vinyl chloride and acrylamide, with or without small quantities of other monomers.

Fibrous substrates, such as paper, are widely used in packaging operations. Paper, however, has a very poor resistance to penetration by water vapor, gases, oil, solvents and greases. To improve the water vapor barrier resistance, paper has been coated with a variety of substances. The most common paper coating is wax. While wax coated paper has good water vapor barrier resistance in a smooth or uncreased condition, it has poor resistance after it is creased. Apparently the brittleness of the wax is so great that creasing causes it to fracture and break thereby providing many areas through which water vapor can pass with little or no resistance. Additionally, wax coated paper does not serve to form a hard and scuff resistant surface.

The coating of paper with asphalt has also beentried and although good water vapor barrier resistance is obtained, the coated paper has poor resistance after being creased. Additionally, asphalt is a black, toxic material which limits its application as a paper coating; particularly in the food packaging industry. Furthermore, asphalt coatings are subject to changes in flow properties with a variance in temperature.

Paper has also been coated with a film of polyethylene. The resulting polyethylene coated paper is found to have less resistance to water vapor penetration that wax coated paper when the coat is tested in a fiat or smooth uncreased condition. The polyethylene coated paper is found to be a better barrier than the wax coated paper when creased.

To improve moisture, oil, solvent and grease resistance, paper has been treated with polyvinylidene chloride. The characteristic brittleness of polyvinylidne chloride causes failures of such coatings with creasing. Attempts to improve this limited flexibility by the use of plasticizers and comonomers with the polyvinylidene chloride results in decreased efficiency of Water barrier properties. The poor impact resistance of the polyvinylidene chloride also results in the rupture of the film during high speed scoring and creasing.

Plasticized polyvinyl chloride polymers are used in paper coating applications. Since the polyvinyl chloride is normally externally plasticized a loss in permanence of the resistance to water, oil, grease and solvents is experienced as a result of the extraction and bleeding of the 'ice plasticizer. The presence of plasticizers also reduces the resistance to the passage of gases and liquids.

In view of the state of the art, it has become highly desirable to discover materials which are useful for coating fibrous substrates which may in turn be useful as packaging materials and will impart good oil, grease, solvent and water vapor barrier resistance.

It is accordingly an object of this invention to provide a material which will provide improved fibrous substrate coating compositions and which may also be used as packaging media.

It is a further object of this invention to provide a ma terial which will provide good oil, grease, solvent and water vapor barrier properties when used as fibrous substrate coating compositions.

Other objects and advantages of the invention will be apparent to those skilled in the art from the following detailed description and claims.

In accordance with this invention it has been found that the above and still further objects are achieved by applying to a fibrous substrate a mixed emulsion comprising a polyvinylidene chloride polymer latex and an ethylene/vinyl chloride/acrylamide interpolymer latex of the type hereinafter described.

The interpolymers which are prepared and used in coating compositions according to this invention in aqeous dispersion or latex form generally contain from about 5 percent to about 70 percent ethylene, from about 30 to about 95 percent vinyl chloride, and from about 0.1 to about 10 percent of acrylamide. Part of the acrylamide in the interpolymer may be replaced by polar monomers such as acrylonitrile methacrylamide, N-(lower alkyl) acrylamide and N-(lower alkyl)methacrylamide containing from 1 to 3 carbon atoms in said lower alkyl groups, N-methylol acrylamide, N[2-(2-methyl-4-oxo-pentyl)] acrylamide, acrylic acid, methacrylic acid, and alkali metal and ammonium salts of acrylic and methacrylic acids, maleic acid, fumaric acid, half and complete alkali metal and ammonium salts of maleic and fumaric acid, aconitic acid, itaconic acid, citraconic acid, and alkali metal and ammonium salts thereof, half alkyl esters of maleic, fumaric, itaconic and citraconic acids having from 1 to 6 carbon atoms in each alkyl group acrylyl and methacrylyl esters of hydroxyalkanoic acids having from 2 to about 6 carbon atoms in the alkanoic acid moieties, acrylylamides and methacrylylamides of aminoalkanoic acids having from 2 to about 6 carbons in the aminoalkanoic acid, hydroxyethyl and hydroxypropyl esters of acrylic, methacrylic, maleic, and fumaric acids, vinyl esters of alkanoic acids having from 1 to 6 carbon atoms such as vinyl acetate, vinyl propionate, and lower alkyl (1 to 6 carbon atoms) sulfonic acid, phenylsulfonic acids, and alkylphenylsulfonic acids and acrylyl and methacrylyl esters of hydroxyalkylsulfonic acids having from 1 to 6 carbon atoms in said alkyl moieties, and hydroxyalkylsulfonamides having from 1 to 6 carbon atoms in said hydroxyalkyl moieties. The acrylamide generally should constitute at least 50 percent by weight of the third or polar monomer of said interpolymer, and preferably constitutes at least about percent of said polar monomer. Thus the interpolymers as prepared in aqueous dispersed form are at least terpolymers containing ethylene, vinyl chloride, and acrylamide, and may be a quaternary or higher polymers containing one or more of the above exemplified additional polar monomers in small quantities but generally such additional monomers will not be present in the interpolymer in quantities greater than about 2 percent by weight.

It is preferred that the interpolymer contain from about 5 percent to about 70 percent ethylene, 30 percent to about percent vinyl chloride, and from about 1 percent to about percent acrylamide. A specific example of choice, as presently understood, is a terpolymer containing from about 18 to 23 percent ethylene, about 72 to about 78 percent vinyl chloride, and from about 2 to about 4 percent acrylamide.

Although the interpolymers used in the practice of this invention are generally unmodified, the modified interpolymers are included for use in this invention. The interpolymers are particularly amenable to hydrolytic modifications by the use of small quantities of a strongly alkaline material such as an alkali metal hydroxide, or a quaternary ammonium hydroxide such as tetramethyl ammonium hydroxide, or by a strong acid such as the mineral acids, e.g. hydrochloric, sulfuric, phosphoric, nitric. The base or acid used preferably has an ionization constant higher than at C.

The hydrolyzing treatment, performed with an acid or a base need not be performed to the same extent, especially if the interpolymer contains polar monomers in addition to the acrylamide. The aqueous dispersion or polymer latex of the ethylene, vinyl chloride, and acrylamide is generally treated with aqueous base or acid in an amount which is chemically equivalent to up to about 100 percent of the amide equival nt in the interpolymer.

Specific examples of polar monomers which may be 2 used, as described above, to replace part of the acrylamide in the polymers of this invention include acrylonitrile, N-methylacrylamide, N-ethylacrylamide, N-propylacrylamide, methacrylamide, acrylic, methacrylic, maleic, fumaric, itaconic, aconitic, and citraconic acids and alkali metal and ammonium salts of such acids, preferably the sodium, potassium or ammonium salts, alkyl esters of such acids, e.g., the methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, butyl methacrylate, ethyl methacrylate, monoethyl maleate, dipropyl fumarate, acrylyl 3-hydroxypropionate, methacrylyl 4- hydroxybutanoate, N-acrylyl acetamide, N-methacrylyl hexamide, 2-hydroxyethyl and 2-hydroxypropyl esters of acrylic, methacrylic, maleic, fumaric, itaconic, aconitic, and citraconic acids, vinyl formate, vinyl acetate, vinyl hexanoate, vinyl and alkyl esters of propanesulfonic acid, vinyl phenylsulfonate, acrylyl and methacrylyl esters of 2-hydroxypropylsulfonic acid, and N-acrylyl and N- methacrylyl 2-hydroxypropanamides.

The ethylene, vinyl chloride, acrylamide interpolymers may be prepared by first mixing ethylene and vinyl chloride in an aqueous medium in the presence of any suitable anionic or nonionic emulsifier and any initiator capable of generating free radicals the chemical mixture at the chosen reaction temperature and pressure. The acrylamide, preferably in aqueous solution either alone or mixed with the appropriate amounts of other polar monomers, is added to the polymerizing ethylene and vinyl chloride mixture gradually throughout the reaction. Since the acrylamide is very reactive, it cannot all be added at the start of the reaction. It is preferable to delay the ad dition of the acrylamide until about to percent of the desired conversion of the ethylene and vinyl chloride has been reached, since, in the final application of the latex, the surface of the polymer particles constitutes the locus of adhesion. This produces a shell-core latex in which the polar monomer is concentrated in the outer layers.

The foregoing ethylene/vinyl chloride-acrylamide interpolymers are readily prepared by various means known to the art. The ethylene/vinyl chloride/acrylamide interpolymers used in this invention are preferably prepared by a process which comprises mixing ethylene and vinyl chloride monomers in the presence of an alkaline buffered reduction-oxidation (redox) initiator-catalyst system, water, and from about 1 percent to about 8 percent by weight based upon the monomer feed, or from about 4 percent to about 7 percent based upon the polymer product of an anionic or non-ionic emulsifying agent having an hydrophilic-lipophilic balance (HLB) value of from about 10 to about 40, and reacting the mixture at a temperature and pressure and for a time sufficient to cause polymerization between the ethylene and vinyl chloride, and then to introduce acrylamide, either alone, or mixed with other monomers in minor amounts in an appropriate diluent such as water into the pressurized polymerizing reaction mixture of the ethylene and vinyl chloride.

The following detailed examples illustrate the preparation of the polymer lattices used in this invention. In the polymer preparation examples, all of the polymerization are carried out in a 3820 ml. pressure vessel at 30 C. at a rotary stirrer speed of 600 r.p.m.

EXAMPLE 1 This example illustrates the preparation of a 21/76/ 3 ethylene/vinyl chloride/acrylamide terpolymer latex, and the post-stabilization of such latex with an emulsifier.

Reaction vessel initial charge G. K S O (KPS) 11.0 NaHCO 15.0 Fe(NG -9H O Tetrasodium ethylenediaminetetraacetate (Na-,EDTA) 1.5 Sodium lauryl sulfate (SLS) H O to make 1700 ml. 1.2 Vinyl chloride (VCl) 450 Ethylene (E) 150 The above ingredient mixture was heated to 30 C. with stirring to give a reaction pressure of 850 p.s.i.g. The polymerization was started by adding a 1 M sodium formaldehyde sulfoxylate-NaHSO -CH O-2H (SFS)/1.5 M ammonium hydroxide (NH OH) solution to the mixture at a rate of 5.2 ml../hr. at the same time 18 ml./hr. of a 25 percent SLS solution was added and the pressure was kept constant by the addition of pure vinyl chloride as required. After three hours had elapsed, a 50 percent solution of acrylamide in water solution was added at 40 mL/hr. The reaction stopped after 5.5 hours and the feed streams were turned off. A total of 1330 g. of VCi, ml. of the 50 percent acrylamide, 27 ml. of the 1 M SFS/ 1.5 M NH OH solution, and 92 ml. of the 25 percent SLS solution had been added. The resulting polymer latex was vented out the bottom of the autoclave. A total of about 3500 g. of the ethylene/vinyl chloride/acrylamide polymer latex was obtained containing 47 percent total This example illustrates the preparation of the base modified ethylene/vlnyl chloride/acrylamide terpolymer.

Using the same reaction vessel and ingredients as are described in Example 1, except that only 10.0 g. of KPS, and only 0.5 g. of SLS was used in the initial ingredient charge. The SFS/NH OH-solution was added at the rate of 4 ml./hr. and the SLS solution was added at 8 ml./hr. The polymerization reaction stopped after 5.75 hours with a total of about 1340 g. of vinyl chloride, ml. of acrylamide solution, 23 ml. of SFS/NH OH solution, and 43 ml. of 25 percent SLS being added. The resultant terpolymer latex was post-stabilized by mixing therewith an additional 17 ml. of 25 percent sodium lauryl sulfate (SLS). The stabilized latex was then vented from the bottom of the reaction vessel. There was obtained 3460 g. of material containing 49 percent total solids, 1 percent of the SLS and essentially the same terpolymer as described in Example 1. The particle size of this polymer latex was somewhat larger than that of Example 1.

This stabilized ethylene/vinyl chloride/acrylarnide terpolymer latex was warmed at 50 C. for 4 to 16 hours 5 after adding 0.4-2.0 g. of sodium hydroxide (added thereto as a 10 percent NaOH in water solution) per kilogram of latex.

EXAMPLE 3 A four monomer component polymer latex was prepared as follows:

A pressure reaction vessel was initially charged with KPS 9.0 NaHCO 12.0 Fe(NOE)-9H O 0.8 Na EDTA 1.5 SLS 0.5 H to make 1700 ml. E 575 VCl 470 This mixture was sealed and warmed to 1550 p.s.i.g. Polymerization was started by pumping into the vessel contents a 1 M SLS/ 1.5 M NH OH solution at the rate of 4 mL/hr. At the same time 10 ml./hr. of a 25 percent SLS was added. Vinyl chloride sufficient to keep the pressure constant was added throughout the reaction. At the end of 3 hours of polymerization an aqueous solution containing 40 percent acrylamide and 10 percent sodium acrylate was added to the reactor at the rate of 24 ml./hr. After 6 hours, the reaction stopped and a total of 591 g. of vinyl chloride, 52 ml. of 25 percent SLS, 27 ml. of SFS/NH OH and 72 ml. of the acrylamide/acrylate solu tion had been added. Unreacted ethylene and vinyl chloride were vented from the top of the reactor to lower the pressure to about 250 p.s.i.g., and then the latex was taken out through the bottom of the reactor. There was thus obtained about 3060 g. of latex containing 43 percent solids, and 1.1 percent sodium lauryl sulfate. The polymer composition was a 21/ 76/ 2.3/ 0.7 ethylene/vinyl chloride/ acrylamide/sodium acrylate polymer. It was suitable for use directly as a coating composition for paper and paper board. The procedure is repeated substituting for the sodiurn acrylate an equivalent amount of sodium methacrylate. An ethylene/ vinyl chloride/ acrylamide/ sodium methacrylate of substantially the same monomer proportions is obtained.

interpolymers prepared in a manner analogous to the procedure described in Example 1 are shown in Table I.

SLS-Sodium Lauryl Sulfate.

The interpolymers prepared in Examples 4 through '6 are modified with sodium hydroxide to obtain hydrolyzed polymer latices having the following solids content:

Latex Example percent No. of polymer Table I sdllds EXAMPLES 12-17 scribed below composed of substantially the same proportion as the product of Example 3.

(12) Component=Hydroxyethyl acrylate Polymer:Ethylene/ vinyl chloride/acrylamide hydroxyethylacrylate 13) Component:N-isopropylacrylamide Polymer:Ethy1ene/ vinyl chloride/acrylamide/ N-isopropylacrylamide (14) Component=N-ethylmethacrylamide Polymer: Ethylene/ vinyl chloride/acrylamide/ N-ethylmethacrylamide (15 Component=A diammonium salt of itaconic acid Polymer: Ethylene vinyl chloride/acrylamide/ diammonium itaconate (16) Component: Monobutyl acid maleate Polymer:Ethylene/ vinyl chloride/acrylamide/ monobutyl acid maleate 17) Component=N-methacrylylpropionamide Polymer: Ethylene/ vinyl chloride/acrylamide/ N-methacrylylpropionamide The polyvinylidene chloride latex and ethylene/vinyl chloride/acrylamide interpolymers latex blends are used in such proportions that, on a solid basis, the ethylene, vinyl chloride, acrylamide interpolymer constitutes 5 95% and preferably 10% to 40% of the final coating with the polyvinylidene chloride polymer constituting the balance. As will be apparent to those skilled in the art, the precise proportions of the two polymers to be employed will vary somewhat depending upon the polymer species employed, but in general, the ratios set forth immediately above will be eminently suitable to achieve the results herein described. The mixed polymer latices employed to coat the fibrous substrates are ordinarily prepared by simply admixing the appropriate latex species. Ordinarily, each of the polymer latices will be initially prepared by an emulsion polymerization process. The terms latex and polymer emulsions are used herein in their conventional sense in which the medium in which the polymers are dispersed is water.

The fibrous substrates to which the compositions are applied in carrying out the present invention include papers of all types, such as bond writing paper, fibrous paperboards such as cardboard, chipboard, carton stock, and the like, wrapping papers or boards, or liners for containers intended for the packaging of foods, greases, chewing gum, soap, soap powders, cosmetics, calking compounds, etc. The coated papers may also be used as wallpapers, papers for lining drawers and shelves, especially in linen closets, kitchen cabinets and the like, and the coated paper or paperboards may be used as bookcovers or book pages.

The coatings may be applied to building construction papers and boards, such as the facing paper on plaster board. It may be used as a release-coating on a paper to be used as a liner in a concrete molding form or adapted to be used for covering freshly-laid concrete roads.

The fibrous substrate, such as paper, which may be coated according to this invention with iblends of polyvinylidene chloride polymer latex and ethylene/vinyl chloride/acrylamide interpolymer latex to produce a product of enhanced barrier characteristics may contain from about 0.5 to pounds of latex blend on one side per ream. (A ream is 3000 sq. ft. and equals 500 sheets, 24 inches by 36 inches.) Generally, however, about 1 to 20 pounds of latex blend per ream is adequate while 1 to 4 pound is all that is needed for many purposes.

The processes for applying the latex blend coating to the fibrous substrate are well known in the art. Such techniques include spraying, roller coating, air-knife coating, trailing blade coating, curtain coater and use of a Mayer rod (machine).

The following examples illustrate the advantageous and unexpected properties which are achieved by the use of the latex blends of the present invention as fibrous sub- 7 strate coating materials, but it is not intended that this invention be limited by or to the examples.

The latex blend is applied to the felt side of the substrate by means of a wire wound rod. Coating rod numbers 6, 18 and 28 are utilized in applying the film. A No. 6 rod has a smaller wire diameter and more winds for a given rod length which deposits a light continuous wet film whereas the No. 28 rod has a larger Wire diameter and fewer winds per inch which deposits a much heavier film.

The fibrous substrate such as paper is mounted on a fiat glass surface, the Wire wound rod is placed in the drawdown bar which is positioned at the top of the sheet, latex blend is then poured across the substrate web just in front of the drawdown bar, the drawdown bar is pulled at a uniform speed across the substrate leaving behind a uniformly even latex film. All coated samples are permitted to air dry overnight, then exposed to 120 C. for 2 minutes, then calendered.

A series of paper sheets were coated With latex blends as shown in Table II containing varying proportions of polyvinylidene chloride polymer and ethylene, vinyl chloride, acrylamide interpolymers. In these examples all parts are parts by weight. The coatings are then tested for various physical properties. The test procedures are hereinafter described and the results are listed in Tables III and IV.

The test methods used to determine the physical properties of the fibrous substrates coated with the latex blends of this invention are listed below along with explanatory notes where necessary. Samples were conditioned according to TAPPI T402m-49 before testing. The paper base stock used in the testing hereinafter described is indicated where applicable for individual examples.

Oil Resistance: Creased box test-A 6" x 6" coated one side specimen blank is folded diagonally from corner to corner, each fold is subjected to a 5 lb. pressure. The blank is further folded one inch from each edge and then made up into a 4" x 4" box having 1" side walls with the coated surface inside. All creases, except those made by the side wall folds converge as an apex in the center of the box bottom. 50 cc. No. SAE oil is poured into the box and the time required to penetrate the creased areas is noted.

Moisture: Vapor transmission rate--A.S.T.M. 3-988 (tropical atmosphere)Reported as grams H O/100 sq. inches/24 hrs. at 100 F. and 90% relative humidity.

each sheet with a No. 6 rod. The Water vapor transmission rates of the coated papers are set forth in Table III.

TABLE III [Moisture vapor transmission rates for coatings of latex blends of polyvlnylidene chloride polymer and ethylene, vinyl chloride. acrylamide inter-polymers] GIBJHSHQO/IUU sq. inches/24 Coating hrs. at 100 F. and 90% R11.

wt., lbs I 1,000 It. 2 Uncreased Greased The oil resistance properties obtained with a series of paper stock of 50 lb. bleached kraft, double coated with a No. 6 rod on one side of each sheet with the compositions of Table II are shown in Table IV.

TABLE IV [Oil barrier properties of latex blends of polyvinylidene chloride polymer and ethylene, vinyl chloride, acrylamide interpolymers] No of penetrations wt.. lb./ Time. Uncreased character- 1,000 ft 2 seconds Greased areas istie 4. 74 660 13 32. 5 4. 42 330 14 14 Flexible. 4. 03 390 10. 5 22. 5 D0. 4. 23 270 9 32. 5 Do. 4. 18 135 8 Do. 4. 90 112. 5 7 37. 5 Do. 4. 78 210 18 100 Do. 4. 185 15 100 Do. 5. 11 160 10 100 Do. 4. 83 117 8 D0. 4. 45 92 9 50 Do. 3. 87 480 13 20 D0. 3. 79 540 9. 5 20 Do. 4. 05 1, 095 4. 5 6 Do. 4. 28 1. 695 O 3 D0. 4. 79 6, 540 0 3 Do.

The results set forth in Tables III and IV show that compositions B through P impart to the paper the desir- TABLE II [Properties of polyvinylidene chloride polymer, ethylene vinyl chloride acrylaxnide interpolymer latex blends Component Latex Latex Latex Percent Visc Example Example Example total cps. at Composition PVD O 1 2 8 solids 5 0 pH A 52. 0 12. 5 3.40 B 52. O 16. 5 4. 45 C- 52. 0 22. 5 5. 10 D 52. 0 30. 0 5. 65 E. 52. 0 55. 5 6. 19 F 52. 0 123. 0 6. 41 G 52. 0 19. 5 5. 98 H 52. 0 62. 5 7. 28 I 52. 0 269. 0 8. .T 52. 0 986. 0 9. 33 K 52. 0 1, 640. 0 9. 62 L 52. 0 16. 5 3. 40 M. 52. 0 23. 0 3. 45 N. 52. 0 37. 5 3. 79 O 52. 0 46. 5 3. 84 P 52. 0 80. 3 3. 86

PVDC-Polyvinylidene chloride-Damn 220-Dewey Almy.

The compositions of Table II were used in preparing a series of coated papers of 30 lb. blue white glassine stock by applying two coats of each composition to one side of r able combination of oil and water vapor resistance and 0 good flexibility. Such combination of properties is not attainable when polyvinylidene chloride polymer is used as the sole coating material.

The replacement of latices 1, 2 and 8 of the compositions B through P with Examples 3 through 7 and 9 through 17 results in coated papers having properties similar to those presented in Tables III and IV. Paperboard such as cardboard, carton stock and chipboard exhibit similar excellent properties as shown in Tables III and IV when coated with the latex blends of this invention.

The paper to be coated can be of a wide variety of types including kraft, bond, parchment, etc. The type, Weight and other physical properties of the paper to which the coating is applied do not significantly offer the improvement in oil resistance and moisture vapor transmission rate brought about by the method of the invention.

The coated papers provided by the present invention have utility for many purposes which will be obvious to those skilled in the art. In particular, the coated papers may be used to wrap food products where it is desired to prevent the transmission of moisture from the atmosphere to the packaged product. The coated papers are easily heat sealed and hold liquids well. As a result, such coated papers can be used in the manufacture of paper drinking cups and the like.

While this invention has been described with respect to certain embodiments, it is not so limited and it is to be understood that varations and modifications thereof may be made without departing from the spirit or scope of this invention.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A fibrous substrate having at least one surface thereof coated with a composition comprising from about to about 95 percent by weight of polyvinylidene chloride polymer and from about 95 to about 5 percent by weight of an interpolymer selected from the group consisting of (a) an interpolymer containing from about 5 to about 70 percent ethylene, from about 30 to about 95 percent vinyl chloride, and from about 0.1 to about 10 percent of at least one other polar monomer including at least about 0.1 percent to about 10 percent of acrylamide, any remainder of said polar monomer content being selected from the group consisting of acrylontrile; methacrylamide; N-(alkyl) acrylamide and N-(alkyl) methacrylamide having from 1 to 3 carbon atoms in each alkyl group; N-methylol acrylamide; N-[2-(2-methyl-4-oxopentyl)] acrylamide; acrylic and methacrylic acid and the alkali metal and ammonium salts thereof; maleic and fumaric acids; half and complete alkali metal and ammonium salts of maleic and fumaric acids; itaconic, citraconic and aconitic acids and the alkali metal and ammonium salts thereof; half alkyl esters of maleic, fumaric, itaconic and citraconic acids having from 1 to 6 carbon atoms in each alkyl group; acrylyl and methacrylyl esters of hydroxy alkanoic acids having from 2 to 6 carbon atoms in said alkanoic acid moieties; acrylamide and methacrylamides of aminoalkanoic acids having from 2 to 6 carbon atoms in each aminoalkanoic acid moiety; hydroxyethyl and hydroxypropyl esters of acrylic, methacrylic, maleic and fumaric acids; vinyl esters of alkanoic acids having from 1 to 6 carbon atoms; alkyl sulfonic acids having from 1 to 6 carbon atoms; phenyl sulfonic acids; alkyl phenyl sulfonic acids having from 1 to 6 carbon atoms in each alkyl; acrylyl and methacrylyl esters of hydroxy alkyl sulfonic acids having from 1 to 6 carbon atoms in each alkyl, and hydroxy alkyl sulfonamides having from 1 to 6 carbon atoms in each hydroxy alkyl, and (b) interpolymers of the type described in (a) treated with an acid or a base having an ionization constant higher than about 10 in amounts equivalent to up to about 100 percent of the amide content of said interpolymer.

2. A fibrous substrate in accordance with claim 1 wherein the interpolymer is a terpolymer containing from about 5 to percent ethylene, from about 30 to percent vinyl chloride and from about 0.1 to 10 percent acrylamide.

3. A fibrous substrate in accordance with claim 2 wherein the ethylene/vinyl chloride/acrylamide terpolymer is treated with alkaline material chemically equivalent to up to about percent of the amide content of the interpolymer.

4. A fibrous substrate in accordance with claim 1 wherein the polar monomer content of said interpolymer is a combination of acrylamide and, under 2 percent of the total interpolymer weight, of an alkali metal acrylate or methacrylate.

5. A fibrous substrate in accordance with claim 4 wherein the interpolymer is a quaternary polymer containing from about 5 to 70 percent ethylene, from about 30 to about 95 percent vinyl chloride, from about 1 percent to about 5 percent of acrylamide, and from about 0.1 to 2 percent of sodium acrylate or methacrylate.

6. A coated fibrous substrate in accordance with claim 1 in which the continuous film comprises from about 60 to about 90% by weight of polyvinylidene chloride polymer and, from about 10 to about 40% by weight of the interpolymer.

7. A fibrous substrate in accordance with claim 1 wherein the substrate is coated with about 1 to about 20 pounds of continuous film on one side per each 3000 square feet of substrate.

8. A fibrous substrate in accordance with claim 1 wherein the substrate is coated with about 1 to about 4 pounds of continuous film on one side per each 3000 square feet of substrate.

9. A coated fibrous substrate in accordance with claim 1 wherein the substrate is paper.

10. A coated fibrous substrate in accordance with claim 1 wherein the substrate is paperboard.

11. Fibrous substrate of claim 1 wherein the polar monomer content of said interpolymer is a combination cf acrylamide and N-methylol acrylamide.

References Cited UNITED STATES PATENTS 3,084,131 4/1963 McEwan et al. 1l7155X 3,310,514 3/1967 Trofirnow et al. 117-155X 3,352,710 11/1967 Wolf et al. l17l6lX 3,428,582 2/1969 Deex 117-161X 3,459,591 871969 Konishi et al. ll7l6lUX WILLIAM D. MARTIN, Primary Examiner M. R. LUSIGNAN, Assistant Examiner US. Cl. X.R. 

